In this specification, the term "vehicle wheel" means a wheel of the type having a hub and a tire mounted on the hub. In general, the hub of such vehicle wheels would be of metal, although not necessarily. Spaced apart side walls extend radially outwardly from a hoop and terminate in a rim. The hoop and side walls form an annular recess for engaging the tire. For convenience, the side walls are referred to as an inner side wall and an outer side wall. The inner side wall is the side wall which in normal use faces inwardly of the vehicle, while the outer side wall faces outwardly of the vehicle. A central plate or spokes are provided within the hoop, and with the hoop form a hub well. The hoop defines the periphery of the well. Such wheels are balanced by attaching one or more balance weights to appropriate balance weight receiving locations. In general, the balance weight locations are provided along the hub rim on the inside and/or outside of the wheel. Such weights attached to the hub rim abut the side wall of the hub adjacent the rim. Alternatively, balance weight receiving locations may be provided at the well periphery and such weights may be secured, for example, by adhesive to the hoop of the hub forming the hub well periphery. Needless to say, it will be appreciated that the apparatus of the invention is not limited to determining parameters of characteristics of such wheels.
Wheel balancing apparatus will be well known to those skilled in the art. Briefly, such wheel balancing apparatus, normally referred to as wheel balancers, comprise a main housing within which is rotatably mounted a wheel support shaft. A wheel to be balanced is mounted fast on the support shaft, which is then rotated. The support shaft may be rotated by a drive motor, or alternatively by hand, depending on the particular type of balancing apparatus. Transducers are provided associated with the support shaft and mountings of the shaft for sensing stresses and strains in the shaft and mountings for in turn determining the out of balance moment of the wheel and the angle through which it acts.
In general, wheel balancers are microprocessor controlled, and they present the data necessary for balancing the wheel on a visual display. Usually the data displayed is the size of the balance weight required to correct the wheel imbalance and the angular position at which it should be mounted on the rim of the hub of the vehicle wheel, where the balance weight is to be hub mounted. Normally, wheel balancers give this information for the inside and outside of the hub rim. So that the size of weight required to correct the imbalance can be correctly determined, it is necessary for the peripheral diameter of the hub rim to be inputted into the microprocessor. It will be readily appreciated by those skilled in the art that the greater the hub rim diameter, the smaller the weight necessary to correct a given imbalance. Further, in most cases, it is necessary to know the distance of either or both the inside and outside side walls of the hub adjacent the rim from a reference plane of the balancer to enable the values of the inner and outer weights to be determined. In general, the distance of the inside side wall from the reference plane and the width of the hub across the side walls adjacent the hub rim is required. Thus, it is necessary for an operator of the wheel balancer to input, generally through a keyboard or by setting programming knobs, the peripheral diameter of the hub rim which is being balanced and the width of the hub across the side walls adjacent the hub rim, and the distance of the inside side wall from the reference plane. Needless to say, where the balance weights are to be affixed to the hub at other locations besides the rim, the radius of these locations and their distances from the reference plane must likewise be entered into the balancer.
Unfortunately, this presents a considerable number of problems, the most serious of which is the possibility of the operator entering the wrong values of these characteristics of the wheel, and of the wheel relative to the wheel balancer. Should a wrong rim diameter be entered, it will be appreciated that while the angular position at which the weight is to be attached, in general, will not be affected, the weight value displayed by the wheel balancer will be incorrect. This, accordingly, will lead to an ill-balanced wheel, which indeed may exhibit imbalance characteristics worse than before it was allegedly balanced. This, therefore, is undesirable. Similarly, more serious difficulties arise if an incorrect value of the other characteristics are entered. In these cases, even the angular positions could be affected.
Attempts to overcome these problems have been made, however, in general, these attempts suffer from a number of disadvantages. In general, such attempts have involved providing a wheel balancer with a device mounted on the wheel balancer to enable the radius of the hub rim and the width of the hub adjacent the rim as well as the distance of the inside and outside side walls of the hub adjacent the rim from a reference plane of the wheel balancer to be entered automatically in the wheel balancer. In general, such devices comprise a feeler member which is mounted on the housing of the wheel balancer and is movable so that an end of the feeler member engages the hub rim. A potentiometer or potentiometers on the feeler member transmit an electrical signal proportional to the distance moved by the feeler member to suitable electronic circuitry. The circuitry computes the rim radius and width as well as distance from the reference plane from the transmitted signals.
These devices have, in general, suffered from disadvantages. In particular, they do not eliminate operator error, and furthermore, they are relatively labor intensive. It is believed that one of the main reasons for these disadvantages is the fact that the feeler member must accurately engage the inside and/or outside rim of the hub in order for the necessary dimensions to be accurately computed by the electronic circuitry. Needless to say, if the feeler member does not correctly engage the hub rim, the signals transmitted by the potentiometer will be incorrect. In practice, it has been found that it is quite difficult for an operator of a wheel balancer to correctly locate the feeler member on the hub rim. In many cases, the inside rim may be relatively inaccessible to an operator due to the construction of the housing of the wheel balancer. Dirt on the hub rim or a slightly damaged hub rim also affects the accuracy of the results. Further, hub rims may be provided with a number of steps, and the operator may engage one of the steps adjacent the hub rim rather than the actual hub rim itself. A further problem with these devices is the fact that because they are essentially mechanically operated, they can wear relatively easily, thus causing backlash, which in turn leads to inaccurate results.
Typical examples of wheel balancers with devices for automatically inputting the hub rim radius and width and the distance of the rim from a reference plane are disclosed in British Patent Specification No. 2,130,386, U.S. Pat. No. 3,741,016 and British Patent Specification No. 2,139,772.
The wheel balancer disclosed in British Patent Specification No. 2,130,386 comprises a device for determining the radius of the inner hub rim only and its distance from a reference plane. The device comprises a feeler member, one end of which is adapted for engaging the inner hub rim, and the other end is mounted on a shaft rotatable in mountings mounted on the wheel balancer housing. The shaft is mounted parallel to the rotational axis of the wheel support shaft and is also slidable longitudinally in the rotatable mountings. The feeler member and shaft are moved outwardly of the housing towards the wheel and the feeler member and shaft are pivoted until the feeler member engages the inner rim of the wheel. A potentiometer is connected to the shaft to monitor the longitudinal distance moved by the shaft when the feeler member is being brought into engagement with the hub rim to determine the distance of the hub rim from the reference plane and a second potentiometer is connected to the shaft to monitor the angular rotation of the shaft caused by pivoting the feeler member and shaft relative to the mountings to engage the rim. Signals from the two potentiometers are transmitted to suitable electronic circuitry for computing the radius of the inner rim and its distance from a reference plane.
U.S. Pat. No. 3,741,016 discloses a wheel balancer with a device for determining the radius of the inner hub rim of the wheel and its distance from a reference plane which is substantially similar to the device of British Patent Specification No. 2,130,386. However, in the case of the device of the U.S. specification, an additional feeler member is provided for determining the distance of the outer hub rim of the wheel from the reference plane so that the width of the hub adjacent the rim may be computed.
British Patent Specification No. 2,139,772 discloses a wheel balancer with a device for determining the radius and width of a hub rim. This device operates on a substantially similar principle to the device of British Patent Specification No. 2,130,386 with the exception that the shaft on which the feeler member is mounted is arranged in such a way that the shaft and feeler member may be moved outwardly of the wheel so that the feeler member is engagable with both the inner and outer hub rims for determining the width of the hub adjacent the rim as well as the radius of the rim.
However, in all cases, these devices require the use of a feeler member which must be positively and accurately engaged on the wheel rim. Thus, it will be appreciated by those skilled in the art that all these devices suffer from the disadvantages already discussed.
There is therefore a need for a wheel balancer which comprises an apparatus and method for determining the radius of one or more balance weight receiving locations of a vehicle wheel and for determining the distance of each balance weight receiving location from a reference plane. In particular, there is a need for a wheel balancer which comprises an apparatus and method for determining the radius of the rim of a hub of a wheel and for determining the distance of a side wall of the hub adjacent the rim from a reference plane. Furthermore, there is a need for an apparatus and method for locating a characteristic of a rotatable member and determining the distance of the characteristic from a reference plane.